let (.()<-) = () and (.{}<-) = () and (.[]<-) = ()
let _ = x.(0) <- 1

let (.%%()<-) = () and (.!!{}<-) = () and (.$+[]<-) = ()
let _ = x.%%(0) <- 1

let _ = (.{}<-)

let _ = x.(0) <- 1 + f x
